#Which terminator?
57 messages in this thread
I'm getting your 4091 SCSI card via a swap of my C= one. Jerry told me I
need an active terminator for my external box that holds 2 drives. Redmond
(West Coast) doesn't seem to know which one I need. At a 15% restocking
fee premium for a custom make jobbie ($52!!!)I'd like to sure to get the
RIGHT thing (for a change <G>). What exactly should I ask for? I'm
assuming this will plug into the female "pass through" plug at end of
ribbon cable that is mounted into back of box.
I'm being very specific because I always get half the information I need
or complete misinformation because it's assumed I know something I need
to, but don't.
Thanks,
Gracia Taking off on AutoPilot from Cooleemee NC
Gracia;
I don't know why you are being told that you NEED an active terminator but
they will improve the signal quality on an Amiga scsi bus. If you also
need a drive, I would suggest just getting one of the Maxtors with active
termination.
A couple of folks at Maxtor were playing with a fellow employee's Amiga
that had always had scsi bus problems. One of the tech's connected a scsi
bus analyzer to the machine. He noted that the bus signals looked
distorted. He then connected a Maxtor MXT-540 (with active termination)
and noted that the signals were quite clean. As they played around they
discovered that it did not matter what they did to the configuration, as
long as the 540 was connect somewhere on the bus, the machine worked fine.
They even removed termination from both ends of the bus and placed the 540
close to the cpu and the bus still worked.
Of course that makes for an expensive "terminator" but it has some "side"
benefits.
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Bill,
I think you just answered your own question! The 4091 uses active
termination onboard. Mixing active and passive termination is definatly
NOT recomended assuming, of course, your data has some value to you. One
of the major difficultys in getting a SCSI bus to operate correctly is
making certain that the termination is right. Passive termination is just
barely able to handle SCSI I data rates, SCSI II FAST is beyond the
capability of passive termination. Therefore we recomend that active
termination is the ONLY supported method of terminating a SCSI bus
attached to the 4091. You must also terminate both ends of the bus, and
ONLY both ends for proper operation. Commodore's original 4091 manual was
rather unclear on this point, which was part of the reason for the
problems some people were having with Commodore's 4091.
Dean
DKB Software
Question?
No question. I was just commenting that the addition of an active
terminated drive to just about any Amiga scsi configuration would improve
performance – even putting the MXT-540 in the middle of a properly
terminated bus slightly improved the signal propagation.
This was all done on a scsi-I bus however.
-bill
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Ah, should have scanned through the messages rather than answering the
first occurrance of your message.
Yes, I had forgotten that Gracia had an A4091!
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Dean –
So if I get a DKB 4091, it has active termination ON IT? And it's
configured so that it is of necessity one end of the SCSI2 bus? But I'll
need to have active termination for the other end of the bus?
So I need either a drive (or other unit) that HAS active termination, and
make sure it's at the far end of the bus, or I need a separate active
terminator, and put IT at the end. Have I got that right?
And everything in between needs all termination removed?
Do other SCSI2-fast controllers have active termination on the board?
Does DKB's 4091 have space for memory on the board?
. . . . JimDoc, on AutoPilot
Jim,
The 4091's SCSI bus is actively terminated on the 4091 itself, but
can be disabled with a switch accessable from the outside of the
machine. IF the 4091 is one end of the SCSI bus, the termination on
the 4091 must be enabled, AND the other end of the SCSI bus must be
actively terminated with all other termination removed. If there are
SCSI connections on both the internal and external SCSI connectors,
then the 4091's termination must be turned off, AND both ends of the
SCSI bus must be actively terminated.
The 4091 also ships with an active terminator intended for use as
the termination for the internal SCSI bus. If you have a drive that
has active termination built in, you can put that at the end of the
bus and ignore the terminator shipped with the 4091. You must also
make sure that all passive termination is removed from the bus.
The only other SCSI 2 FAST host adaptor for the Amiga that I am
aware of at this time is the Fastlane, and it uses passive
termination only.
The 4091 is a SCSI adaptor only and has room on the board for an
inch high hard drive.
Dean
DKB Software
Bill,
Thanks for info. Gerry, who I assume *IS* DKB, told me I "needed" an
active terminator. I have an external box with a CD ROM & tape dr,one of
which is, of course, terminated. I guess I'll wait till I get new DKB 4091
back & try it that way. So far I have had no luck with my old 3000 & the
C= 4091 in 4000. I NEED more HD space!!!!
Just saw your tag & ROFL. I've been playing with a kid's 486 w/wondoze. He
asked if he was seeing things or was my machine much faster <G>? You
wouldn't believe the brain dead paint & image programs on it.
Gracia Taking off on AutoPilot from Cooleemee NC
Gracia;
Yep, Mike Sinz saw that and posted it (on another network) stating that it
was directly from a MicroSoft advertisement. I "about died" laughing and
figured that I would borrow it for awhile <g>
Amiga scsi performance (even the 2091/A3000) has always pushed the ability
of the bus and drives. One of the reason why people often have trouble
with some of the drive hardware on the Amiga is that the hardware is not
always up to the speed of the Amiga scsi bus and the termination was
"iffey" at those speeds.
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Bill,
You mean it isn't always good to be the fastest & the best ;^}.
Gracia Taking off on AutoPilot from Cooleemee NC
Well, I wouldn't go so far as to say that. Now then, you do have to be a
little careful where you are, and who might be listening when you shout "I
want more SPEED!" You might find yourself in the continous company of
NARCs. 🙂
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Bill –
> …an active terminator but they will improve the signal quality on an
> Amiga scsi bus.
Where does one go to purchase an active terminator to apply to one's bus?
. . . . JimDoc, on AutoPilot
Well, Jim… the only ways that I personally know of for sure to work are:
1) Buy an A4091 from DKB or
2) Buy a drive with active termination
Now of course, either of those is silly if you don't need a drive or
controller. There must be someone around who has them but I don't know
who 🙂
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Jim,
Redmond cable has active terminators. I've also seen a few other
catalogs that list them. The biggest headache is making certain you
get one with the proper connector on it. There are three basic SCSI
connectors that are available, and one connector that should never
have been used.
The three correct connectors:
50 pin high density SCSI 2. (same size as a serial connector but many
more, much smaller pins. This is the external connector for the 4091)
50 pin ribbon cable connector. (This is the standard internal SCSI
connector method)
50 pin centronics type connector. (Looks like a oversized printer
connector. This is what most good external boxes use.)
The bad connector that should _never_ be used for SCSI 2 FAST:
DB25 connector, commonly known as the MAC SCSI connector. (This
particular connector is the reason for many SCSI problems that people
run into. Aviod it like the plague on a SCSI 2 FAST bus!)
Dean;
>… that should never have been used.
Well stated. However, you should not have later qualified the limit by
saying SCSI-II. That miserable connector has been the source of more
Amiga SCSI problems than probably all other problems combined.
(of course with SCSI-II, I think I would be surprised if a bus having that
connector anywhere in the chain would work at all under the best of
conditions)
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Bill,
Ideally, we would never have to use the DB25. However most people don't
have a choice when it comes to SCSI I external boxes. (reality intrudes!)
Unfortunatly, the DB25 connector appears to work with most SCSI I
implementations, it's generally those people who start adding more than
one device on the bus who run into the brick wall at 90 mph.
SCSI II FAST on the other hand should never use the DB25 connector. If
anyone does, they deserve all the grief they get! 😉
Dean
DKB Software
Dean;
I have two internal and five external scsi devices on this machine. The
connection to the Amiga is via an 24 inch blue ribbon to DB-25 cable. I
can tell you that I went through a bit of grief finding a cable that would
work (even that short).
I figure that there are already enough "gotcha" with the potentials for
formatting errors, drive errors, termination problems and the like without
adding improper cable and connector design.
I am BTW, not even remotely surprised that the DKB controller uses the
correct connector.
-bill at least they got this right:
"The less you know about computers – the more you want Microsoft Windows"
Bill,
Is that 24in cable a 50 conductor, or a 25 conductor? There are 50
conductor round cables that terminate on one end as a DB25 and on the
other as a 50pin centronics. This would probably be the best solution
unless your external boxes use DB25's.
There are some configurations where the DB25 is the only practical
solution. SCSI II FAST is _not_ one of them! Certainly a low end SCSI
interface where the most likely external boxes are MAC type drives is one
of those configurations.
Dean
DKB Software
Yes, my cables are all 50 conductor regardless of the number of
connector pins. The "bargain" Mac cables (25 conductors) are a real
disaster.
Dean –
> SCSI II FAST on the other hand should never use the DB25 connector.
Do you know what "flavor" or SCSI-2 the PP&S Zeus uses? It DOES have the
DB25 connnector on the "back-of-the-box" end of the board.
. . . . JimDoc, on AutoPilot
I have no idea what the Zeus uses. Sorry. 🙁
>The bad connector that should _never_ be used for SCSI 2 FAST:
>
>DB25 connector
Why is that? Is it because people may connect it to the wrong ports or is
there another reason?
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
For proper operation, particularly those that use cables longer
than three feet, SCSI cables need at least one ground return wire for
every data and control signal on the bus. Since there ar 18
data/control signals on a SCSI bus plus termination power, a 25 pin
connector simply doesn't have enough pins to supply what the bus
needs. (You can thank Apple for this non-standard connector)
The end result of using this connector and the cable that attaches
to it is unreliable data transfers that gets worse as the total cable
length grows. A better solution for external drives is the Centronics
50 pin connector, or in the case of SCSI II FAST, the 50 pin
hi-density connector.
>The end result of using this connector and the cable that attaches to it
>is unreliable data transfers that gets worse as the total cable length
>grows.
Thanks for the info. Since the Amigas have the 25 pin port for SCSI, is
there a problem adding fast SCSI drives externally? I have a external PC
box that I had added a SCSI drive to using the MAC DB 25 to Centronics
cable then attaching to the box. Is this the best way to connect it?
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Tony,
As long as the cable has 50 conductors, you keep the total cable
length short (less than 6 feet), and you properly terminate both ends
of the bus, you should be OK. None of the builtin SCSI adaptors are
SCSI II FAST, so you won't be using the fastest data rates. If you
run into random data errors or SCSI bus problems, going to active
termination can help dramaticly.
If your SCSI adaptor has a DB25 connector, the best thing to do is
to convert that into a centronics connector and a 50 conductor cable
as soon as possible.
Dean
DKB Software
>If you run into random data errors or SCSI bus problems, going to active
>termination can help dramaticly.
What do you mean by `active termination'? As opposed to what?
I know how to terminate a SCSI chain but I never hear that specific term
before.
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Tony,
There are several different methods of terminating a SCSI bus. One
is passive termination, which is the type that most people are
familiar with, another is active termination. Active termination is a
more complex terminator, with the advantage of adapting itself to the
current bus condition. Passive termination, as the name implys, just
sits there doing it's job, but tuned for the average case. Problem
is, the average case doesn't really exist.
There are other termination methods, a particularly significant one
is 'forced perfect termination' promoted and used by IBM drives.
While the termination method seems to work well, it does not appear
to be compatable with other termination methods, or most SCSI
interface chips. It was not, to my knowledge, ever condoned by the
standards commitee. For that reason, I do not recommend using IBM
drives with the 4091.
Thanks for the explanation of active termination.
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Dean,
I've been hearing of active terminators for years and have never been able
to find one! The closest was a SCSI break-out box with data analyzer for a
few hundred with selectable active termination. But I imagined a little
plug with some electonics inside powered by the tpwr line. 'Cept in GVP's
case you are SOL cause they chose not to implement this line and your
devices must supply it if you expect to get it.
wmc – via Autopilot!
Wayne,
Active terminators are available from Redmond Cable as well as quite a
number of other places. They haven't been generally available until just
recently.
Dean
DKB Software
Dean,
Do they look much different than the old terminator blocks? What about
cost? (My local dealers have lots of the SCSI-II FAST cables with the
mini-50 pin to centronics, and the old terminator blocks, but when I ask
about active terminators I get blank stares…. can't even get them to
look at the catalog for them.)
wmc – via Autopilot!
No. The connector should never have been used for SCSI period
(including SCSI-I). The inadvertant connection problem is certainly
yet another consideration but not the primary one.
The problem is that even SCSI-I bus speeds are high enough that you
need a good quality "transmission line" for the signals. The 50 pin
bus connectors provide this. The 25 pin is a kludge (and a poor one
at that).
Apple Macintosh started the whole thing of using a DB-25 for SCSI. On
the Mac, the machine was quite slow (by scsi standards). When the
Amiga came alone, they used the DB-25 for cost reasons but they also
designed the fastest microprocessor based SCSI machine that the world
had seen.
The Amiga A2091/A3000 SCSI was fast enough that the marginal
performance of the DB-25 became a serious issue. Even drives that
are slightly marginal will often not work on an Amiga (or be
"flakey") and yet be "solid" on other machines.
With SCSI-II the problem is hopeless as far as the DB-25 is
concerned. SCSI-II command/data duration is way too low for any
sloppy design (the same reason that active termination is not an
option on SCSI-II).
>The Amiga A2091/A3000 SCSI was fast enough that the marginal performance
>of the DB-25 became a serious issue. Even drives that are slightly
>marginal will often not work on an Amiga (or be "flakey") and yet be
>"solid" on other machines.
Maybe this is the problem I had when I tried to add a external SCSI HD to
my A3000, it was nothing but trouble.
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Could very well be the case. I have (or have had) eight machines
with A2091 controllers. Certain external drives always worked no
matter which machine they were on IF connected by themselves. Thus,
when SCSI "problems" came up, I would eventually get to the point
where I would connect just the one external drive. If that worked
then I knew that the basic machine was "OK."
One thing that does "throw" people now and then; I have had the
problem four times (that I know of for sure), is that drives can have
data in the RDB area of the disk that "freezes" the machine (actually
the ROM based scsi.device). Though there is more than one way to
solve the problem, the easiest way that I have found is to power down
the system, remove power to the drive, reboot, power up the drive and
then use HDToolBox to install a valid RDB.
>Certain external drives always worked no matter which machine they were
>on IF connected by themselves.
I'll have to keep that in mind if I ever get any more SCSI problems. (what
do I mean `if'? :^)
Btw, I have dealt with 3.5" drives and their thin terminators. Are
terminators for 5.25" drives different? I had a 5.25" Full height drive
and couldn't find terminators nor where they plug into.
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Tony;
That's what I like! The eternal optimist!
The 3.5" drives almost universally use the "single inline" style package
for the terminating resistors but it is primarily a matter of when the
drive was designed.
The other format for the resistors is a package that looks like a "run of
the mill" TTL chip. Usually dual inline, 14 pin.
The "package" usually "stands out" to those familiar with IC packages. It
may be a different color or appear to have a different "luster" if the
same color as the IC packages. Additionally it will have a decidedly
different numbering style. Also recognizing a resistor manufacture's logo
can help.
-bill
>The other format for the resistors is a package that looks like a "run of
>the mill" TTL chip. Usually dual inline, 14 pin.
I think I saw 2 of them (1 on each corner) on the 5.25" HD I had and I
thought that these maybe the terminators but wasn't about to mess with
it.
Thanks for the lesson.
<<< Tony D. Tracer >>>
(Any render time >0 needs acceleration.)
Gracia,
The first thing I need to know is what type of connector does your
external box use for the SCSI cabling? Is is similar to the connector on
the back of the 4091? Or is it a much larger 50 pin 'Centronics' connector
similar to, but larger than, what is on most printers? If the connection
is a DB25, ie. a MAC cable type, there may be a problem getting the proper
termination.
The most common type of connector is the Centronics type, which Redmond
does have, as we bought one from them last year. Thier description lists
it as a 'SCSI I ACTIVE SINGLE SID'. If you have a different type of
connector, let me know and I'll see about helping you get the right one.
Dean
DKB Software
Dean,
External box has 50 pin female centronics at both ends. I just spent $52
getting a tiny DB50 male to 50 centronics cable, since C= 4091 has the
tiny DB(?)50 pin female out & box has 50 centronics in (& out). Will it
ever end <G>. I know SCSI is a Art form, but this is getting ridiculous.
Aside from the $ I've spent in last 1 2/2 yr with no SCSI to show for it
I am left with out the use the 2 drives, HD space & decent backup. Since
even my techie in Winston can't get it working it's not just me being a
"dumb broad" ;^}.
Gracia Taking off on AutoPilot from Cooleemee NC
Gracia,
$52 for a SCSI 50 to centronics 50??? That should be a rather standard
cable these days.
The terminator you need is a SCSI I (centronics 50 was supposed to be
the SCSI I standard connector) Active terminator. We have gotten exactly
this connector from Redmond Cable, so I am sure you can get one there.
Dean
DKB Software
Gracia:
That 4091 _should_ have come with a small PC board that is an _internal_
active terminator. (It's a little 1×3" board – there's a hole on the 4091
PC board of the same size.)
You could hook it up to the end of the SCSI cable on your external box,
maybe? (You're beginning to realize why I bailed out of the SCSI-II pool
so quickly? :^)
BTW, APS (the drive co.) is selling their new drives in an external case
with some kind of 'magic terminator' – it's probably an active terminator.
You might want to consider that (if you'll be buying any external goodies
in the near future.)
Good Luck,
Keep On Toastin'
Erik Flom
Hi Erik,
I sent that "little PC board" to DBK along with 4091 for swap as
requested. It goes on 4091 inside 4000, I assume (yah, I know what that
makes you & me <G>). BUT I understand one must have a terminator at end of
line on last dr. in external box…or as Jerry at at DKB told me, an
active terminator that plugs into the pass through end plug of box. HELP!
I'm caught in a SCSI controller & can't get out!!! I'd bail out also if I
didn't already have the 4091 & 2 SCSI drives. By now they're so old
they're out of date ;^}! Thank heaven they've made a tougher gun law, I'm
ready to take aim.
Gracia Taking off on AutoPilot from Cooleemee NC
My sincere condolences on your SCSI-hell.
I remember hearing of your problems before I even owned a 4000, now to
think that my actions have caused you further pain!
But seriously, I thought the active terminator was for the end of your
SCSI chain? Oh well, looks like you might want to buy a new drive, just to
get a free active terminator with it. :^)
Good Luck,
Keep On Toastin'
Erik Flom
Since I need more HD, it's not such a crazy idea <G>!
Gracia Taking off on AutoPilot from Cooleemee NC
Hi Erik, I just received the March AmigaWorld and saw another one of your
great 3D renderings. I just thought I'd drop you a line to say it looks
great.
Jim R. Ollick
Using AP from Bergenfield, NJ
Great! Thanks! I guess I'll have to run out and buy an issue.
They were supposed to use 2 small screen shots on the front cover, and
a larger shot of the earth in a 2-page spread. (Unfortunately, I did
it _before_ I got that real cool luminosity map, so the earth is
kinda boring in the image…..:^)
Keep On Toastin'
Erik Flom
There were 2 shots on the cover, yours and one from Dave Thomas. On pages
22 and 23 there is a shot of your earth with an article by Dave "RX for FX
… Very Special".
Jim R. Ollick
Using AP from Bergenfield, NJ
Gracia: You should have received an 'active' terminator with your CBM 4091
board, at least I got one with mine. It's a small circuit card with a
couple of chips and a 50-pin SCSI connector. Also marked as "SCSI II
TERMINATOR BD REV A". So at the end of your SCSI chain on your external
box, just plug this terminator in and you should be all set.
// John – (Who enjoys harrasing the vendors)
\X/ Mercury@ins.infonet.net
John,
I did indeed get that card & I set it with board to DKB for swap, as I was
advised. I was under impression that this was for internal board
termination & the last drive in chain also needed one, at least that's the
information I got from Jerry at DKB. One day I'll get all the right moves
<G>.
Gracia Taking off on AutoPilot from Cooleemee NC
Gracia,
The terminator that is shipped with the 4091 is to terminate the
internal cable if used. There is a terminator on the 4091 itself, which
normally handles the other end of the chain, _unless_ you also have
something connected to the external connector. In this case (something
connected to both the internal and external connectors) you will need to
disable the terminator on the 4091 and add a terminator to the end of the
external chain. If you don't have any of your drives connected internally,
and your external case has a 50 pin ribbon cable connector at the far end
of the cable, you could use the terminator sent with the 4091 to terminate
the external chain.
Dean
DKB Software
Dean,
I have just had a real female crying jag!! I am so frustrated with this
SCSI problem I could do real harm. Not one piece of equipment seems to fit
with another and so far nothing works. FOR 1 & 1/2 YEARS!! First not with
the 3000 & now the A4091 SCSI card. I've spent a fortune & not had any
satisfaction. I don't know what I shall do when I find out your SCSI card
doesn't work. At least it will be consistent <G>.
Gracia Taking off on AutoPilot from Cooleemee NC
Gracia,
Please send me a list of the SCSI drives you have been fighting with.
I'll see what we can find out on this end.
Dean
DKB Software
Since I have waited this long for my drives to work I guess I can
wait till I get board back & see if it at least shows up on the
computer & then tackle the job of getting drives to work. Maybe a
miracle will happen. I don't think it's the drives, it's getting a
controller for the 4000 to work, then I can go from there.
Actually, if you were going to install internal drives in your 4000, then
you would use the supplied terminator to terminate those drives. However,
I'm under the impression that all of your SCSI drives are going to be in
an external box, so the supplied terminator could have easily been used
for that purpose. I'm sure DKB will get the job done for you and use the
terminator as needed.
// John – (Who enjoys harrasing the vendors)
\X/ Mercury@ins.infonet.net
I'm reaching the point of no return..,picking up everything & throwing it
out the window!!!
Gracia Taking off on AutoPilot from Cooleemee NC
"I'm reaching the point of no return..,picking up everything & throwing it
out the window!!!"
Just let me know when you plan on doing this Gracia, I want to be below
your window to catch it all <g>. Seriously though, I'm sure Dean and his
crew will get things right for you so I won't try to confuse you anymore,
well, at least not today.
// John – (Who enjoys harrasing the vendors)
\X/ Mercury@ins.infonet.net